Aircraft wheels are currently designed primarily in response to requirements for accommodating selected tires as well as housing the aircraft's brakes and supporting the aircraft on a ground surface. A goal is to accomplish these functions with a wheel design that adds a minimum amount of weight to the aircraft while maximizing wheel operational life. Aircraft wheels not only help support the aircraft's weight during taxi, but, along with other landing gear structures, are required to absorb significant loads when an aircraft lands. The conditions under which aircraft wheels must operate during service, moreover, may be harsh and demanding. Aircraft wheels typically experience not only high energy braking events that can produce significant heat, but also may be subjected to carbon dust from the application of carbon brakes and fluids from the runway and aircraft. Consequently, the United States Federal Aviation Administration (FAA) and corresponding international aircraft regulatory bodies require that each aircraft main and nose landing gear wheel be submitted for approval prior to use on an aircraft. The FAA reviews such factors as maximum static and limit load ratings of each wheel, taking into consideration design maximum weight and critical center of gravity. The maximum limit load rating, for example, must equal or exceed the maximum radial limit load determined under applicable ground load requirements of the wheel. Additional requirements apply to wheels with brakes.
Aircraft landing gear wheels include bearings or bearing structures that connect and support various parts of an aircraft wheel. In comparison to the total time period when an aircraft is operating, bearings function or are loaded relatively briefly. During bearing loading phases, aircraft wheel bearings must operate with maximum reliability while they absorb extreme forces and torques, initially when the aircraft lands and then when the aircraft is taxiing. The use of aircraft brakes during taxi also applies loads on wheel bearings. It is essential that the bearing structures used in aircraft wheels be capable of operating reliably under these conditions. It is, additionally, desirable that such bearings be as lightweight and low maintenance as possible.
A variety of different bearing structures designed for use in aircraft landing gear wheels has been proposed. The location of these bearing structures depends on the type of aircraft wheel. For example, in one type of wheel configuration, known as an A-frame design, the two wheel parts are fastened together under a tire-supporting rim, and bearings are provided only where the two wheel parts contact a landing gear axle. This type of wheel leaves very little space for brakes or other structures between the tire-supporting rim and the axle. Another type of wheel configuration known as a bowl-type design provides the space needed for aircraft brakes or other structures. For large aircraft with high brake energy and heat sink requirements, however, a bowl-type wheel, although it increases an aircraft's weight, may meet these needs. This type of aircraft wheel, which usually includes multiple wheel sections, requires bearings both adjacent to the landing gear axle and between wheel parts adjacent to the tire-supporting rim of the wheel. Aircraft landing gear wheels that are essentially bowl-type in configuration to accommodate an aircraft's brakes within the wheel between the axle and tire-supporting rim and have bearings only on the axle side of the wheel are described and shown in U.S. Patent Application Publication No. 2010/0202791 by Dotzel et al. While this arrangement accommodates the wheel brakes substantially within the wheel volume, the various arrangements of the two-part wheel shown have vertical sections that require one or more fasteners to secure the parts of the wheel assembly as well as apparently to provide stiffness to the wheel. In U.S. Patent Application Publication No. 2010/0290731, Proeschel et al also show and describe aircraft wheel bearing structures located only adjacent to an axle and not adjacent to a tire-supporting rim. The wheels of Proeschel et al, however, also have structural elements that substantially fill the volume between the axle and the tire-supporting rim, including fastening structures that hold wheel parts together. The aircraft wheel braking system disclosed by Souetre et al in U.S. Pat. No. 7,124,860 has a centering bearing supporting brake structures that can be constructed with alternating zones of materials of different stiffness. None of the foregoing published patent applications or patent, however, suggests that a bearing arrangement in an aircraft landing gear wheel in which bearing structures are effectively located only in a part of the wheel adjacent to an axle without additional structure required to fasten wheel sections and provide structural integrity.
Providing motors and other drive devices to move aircraft independently on the ground without reliance on the aircraft's main engines or tow vehicles is known. Such motors and drive devices may be installed in aircraft wheels to drive or power the wheels and thereby move the aircraft during taxi. In U.S. Pat. No. 7,445,178, for example, McCoskey et al describe a powered nose aircraft wheel system with a traction motor mounted in an A-frame type wheel that rotates the wheel to drive the aircraft on the ground. Bearing structures are located only adjacent to the wheel axle, and the structures required to join and fasten the sections of the A-frame wheel completely fill most of the space between the tire rim and the axle. Wilson, in U.S. Patent Application Publication No. US2011/0089289, describes mounting an electric motor in a two-part bowl-type aircraft main wheel in space normally occupied by brakes to drive the aircraft during taxi, but does not show or describe bearing structures. An alternate location may be required for brakes. Neither McCoskey et al nor Wilson suggests an aircraft landing gear wheel configured with effective bearing structures positioned in a bowl-type wheel that maximizes volume within the wheel and provides optimal structural integrity to the wheel.
A need exists, therefore, for a bearing arrangement for an aircraft landing gear wheel that provides effective bearing support for the wheel while maximizing internal wheel volume available to incorporate a wheel drive means or other structures and optimizing wheel stiffness and structural integrity.